I. Field of Invention
This invention relates to the field of manufacturing technologies for aeronautical parts and particularly the sector of transportation tools for transporting such parts between manufacturing stations.
II. Prior Art of the Invention
In the manufacture of aeronautical parts, the handling of each of the parts during its manufacturing stages is currently very varied and depends on the specific process of manufacture being used. Among such parts to be found are large size parts such as wings, stabilizers, fuselage panels, rudders, etc., and parts thereof, such as their coverings. In order to handle these parts and their transportation between the various manufacturing stations which they have to pass through, there exists a wide range of tools, trolleys, stocks, etc., for being able to handle the parts depending on the state or phase of manufacture that the parts are to be found in at any moment.
Nowadays, carbon fibre based materials are more and more prevalent than aluminium for aeronautical coverings. Such coverings are typically manufactured as follows.
First, the covering is taped to a tool generally made of Invar. The taping is a process consisting of locating layers of reinforced composite material in the form of strips on a mold in different directions in order to obtain the desired properties. An example of a composite material widely used in the aeronautical industry is preimpregnate, a mixture of fibrous reinforcement and a polymer matrix used for manufacturing composite materials in such a way that it can be stored for later use. In this process, the strips are not placed randomly; instead, they are generally laid or deposited in certain directions, specifically, at 0°, 90°, 45° and −45°. The number of layers (thickness) and the depositing of the strips in certain directions or others is determined according to the nature and magnitude of the stresses which the part is going to withstand at each point.
Following the taping, it is necessary to confer stiffness on the covering, for which a structure of horizontal and vertical stiffeners is used. In order to locate the stiffeners in the right directions in the coverings, certain modules with different geometries are used, arranged matrix-fashion, between which the horizontal and vertical stiffeners are introduced. Initially, the modules are located in a tipping frame and the stiffeners are introduced between them. Afterwards, the frame is rotated, and the entire array (stiffeners and modules) is located on the covering in the proper position; on this array a bag is located with which a vacuum will be created in order to prevent porosities and then the entire array (tool+covering+stiffeners+modules+vacuum bag) is then introduced into an oven, known as an autoclave, in order to provide the part with the desired characteristics. The autoclave is usually a horizontal cylindrical tank in which the parts are introduced, with a door at one of its ends and a fan plus the heating and cooling system at the opposite end. The autoclave is charged with compressed air plus nitrogen up to the required pressure, depending on the curing cycle of the parts, and the mixture (air+N2) is then recirculated inside by the fan in order to heat up the parts, the temperature being reached and maintained with the heating system (an array of resistors) or cooling by means of the cooling system. By this stage, it is possible to cure the parts.
Following the curing, it is necessary to withdraw the vacuum bag and the modules for the covering. The vacuum bag is withdrawn by hand. After that, the mold stripping or withdrawal of the modules located on the covering is carried out. The last two stages consist of edging and ultrasound inspection. Once the edging phase is completed, the part has to be transported to the automatic inspection machine where it is positioned and secured in the right position for carrying out non-destructive inspection of the part. By means of this stage, the intrinsic quality of the element is defined without damaging it, in other words, a definition is made of whether it has any problems regarding later use. For these tests, inspection equipment is used that is capable of detecting any discontinuities that might be present in the material being used (in this case, carbon fibre) and recording them without damaging the part.
As a final stage, if the entire manufacturing process has been passed through correctly (no manufacturing defect has been detected in the part), the part will be taken to the parts dispatch warehouse or, if any defect was detected in the inspection, the part will be taken to the repair zone so that the necessary operations can be carried out there for rectifying the part.
Each of these stages generally use different transport devices, involving not just the cost of purchasing and maintenance of these devices but also the fact that these devices are used sporadically and discontinuously, plus the fact that they generate handling times which increase the work and slow down the manufacturing process.
For that reason, it was desirable to overcome the drawbacks described above and achieve a handling of parts that would permit the manufacturing costs of the aeronautical parts to be reduced by saving handling times which do not add any value to the part. This was particularly desirable in view of the fact that the rate of manufacture of aeronautical parts, which did not usually very high in comparison with other sectors, has now increased notably and the forecast for the coming years is that it is going to increase even further.